lnwallet: update reservation workflow to revoke keys
lnwallet: update reservation workflow to revoke keys

With this commit, the reservation workflow for the single funder use
case is now aware of the usage of revocation keys.

The changes are relatively minor:
  * contributions now have RevocationKeys instead of RevocationHashes
  * CompleteReservationSingle now takes the initiators revocation key

ddustin/lnd,ddustin/lnd,AndrewSamokhvalov/lnd,BitfuryLightning/lnd,bryanvu/lnd,BitfuryLightning/lnd,LightningNetwork/lnd,aakselrod/lnd,bryanvu/lnd,aakselrod/lnd,AndrewSamokhvalov/lnd,LightningNetwork/lnd